U.S. patent number 4,866,909 [Application Number 07/186,649] was granted by the patent office on 1989-09-19 for high tensile wrapping process.
This patent grant is currently assigned to Lantech, Inc.. Invention is credited to Patrick R. Lancaster, III, William G. Lancaster.
United States Patent |
4,866,909 |
Lancaster, III , et
al. |
September 19, 1989 |
High tensile wrapping process
Abstract
A film web is dispensed from a film web dispenser and wrapped
around a bundle by moving the bundle into an applicator mandrel,
revolving the film web dispenser relative to the applicator
mandrel, dispensing the film web from the film web dispenser on to
the applicator mandrel at a constant supply speed. The film web,
wrapped around the applicator mandrel, is transported beyond the
downstream end of the applicator mandrel, the bundle is moved
beyond the downstream end of the applicator mandrel and the film
web is applied from the applicator mandrel onto the bundle so as
provide a containment force in the film web after it is applied
onto the bundle. A dual stage wrapping system is used in such a
manner that each orbinting dispenser is restrained to dispense the
film web at a constant supply speed less than the lowest film
demand speed at the applicator mandrel and independent of the
tension on the film web between the film web dispenser and the
applicator mandrel. The applicator mandrel is positioned to resist
crushing or disalignment of the bundle or subunits of the bundle
within the applicator mandrel and also modified its position to
modify the wrapping cross-section of the bundle so that the web
strain elongation varies substantially within a linear wrap force
range above the yield point of the stress strain characteristics of
the film web between the film web dispenser and the applicator
mandrel.
Inventors: |
Lancaster, III; Patrick R.
(Louisville, KY), Lancaster; William G. (Louisville,
KY) |
Assignee: |
Lantech, Inc. (Louisville,
KY)
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Family
ID: |
26882292 |
Appl.
No.: |
07/186,649 |
Filed: |
April 19, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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804542 |
Dec 4, 1985 |
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582779 |
Feb 23, 1984 |
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Current U.S.
Class: |
53/399; 53/556;
53/449; 53/588; 53/441 |
Current CPC
Class: |
B65B
11/008 (20130101) |
Current International
Class: |
B65B
11/00 (20060101); B65B 013/12 () |
Field of
Search: |
;53/399,441,449,556,587,588,176 ;156/428,430 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0096635 |
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Dec 1983 |
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EP |
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144266 |
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Jun 1985 |
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EP |
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0152959 |
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Aug 1985 |
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EP |
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3338038 |
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May 1985 |
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DE |
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Primary Examiner: Sipos; John
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner
Parent Case Text
RELATED APPLICATION
This application is a continuation, of application Ser. No.
804,542, filed Dec. 4, 1985 now abandoned which is a
continuation-in-part of copending application Ser. No. 582,779
filed Feb. 23, 1984, now abandoned which is incorporated by
reference into this application.
Claims
What is claimed is:
1. A process for stretch wrapping a bundle with a film web
dispensed from a film web dispenser comprising:
moving the bundle into an applicator mandrel having a noncircular
cross-section;
revolving the film web dispenser relative to the applicator
mandrel;
dispensing the film web from the film web dispenser at a
substantially constant supply speed by preventing the supply speed
of the film web at the film web dispenser from increasing and
preventing the supply speed of the film web at the film web
dispenser from decreasing;
stretching the film web in the direction in which it is
dispensed;
wrapping the stretched film web onto the applicator mandrel;
transporting the film web wrapped around the applicator mandrel
beyond the downstream end of the applicator mandrel;
continuing moving the bundle beyond the downstream end of the
applicator mandrel; and
applying the film web from the applicator mandrel onto the bundle
so as to provide a containment force in the film web after it is
applied onto the bundle.
2. A process as claimed in claim 1 including revolving the film web
dispenser around the applicator mandrel.
3. A process as claimed in claim 1, wherein the revolving step
includes revolving the film web dispenser about the applicator
mandrel and the bundle at a rate of at least about 30 revolutions
per minute.
4. A process as claimed in claim 1, wherein the revolving step
includes revolving the film web dispenser about the applicator
mandrel and the bundle at a rate in a range of about 40 to 60
revolutions per minute.
5. A process as claimed in claim 1, including controlling the
supply speed of the film web with a motor and a motor controller
having regenerative capabilities.
6. A process as claimed in claim 1, including moving a bundle
having a non-circular cross-section into an applicator mandrel.
7. A process as claimed in claim 1, including preventing the film
web from substantial pre-stretching prior to dispensing the film
web from the film web dispenser onto the applicator mandrel.
8. A process as claimed in claim 1, including positioning a
substantially oblong cross-sectioned bundle in the applicator
mandrel and preventing the film web from substantial pre-stretching
prior to dispensing the film web from the film web dispenser onto
the applicator mandrel.
9. A process as claimed in claim 1, including substantially
pre-stretching the film web in the film web dispenser prior to
dispensing the film web.
10. A process as claimed in claim 9, including pre-stretching the
film web at a constant pre-stretch ratio in a range of about 2:1 to
3:1.
11. A process as claimed in claim 1, including pre-stretching the
film web in the film web dispenser prior to dispensing the film web
when wrapping a bundle having a substantially square
cross-section.
12. A process as claimed in claim 1, including restraining and
retarding the film web being dispensed by the film web
dispenser.
13. A process as claimed in claim 1 including dispensing the film
web from the film web dispenser at a rate independent of the force
on the film web between the film web dispenser and the applicator
mandrel.
14. A process as claimed in claim 1, including dispensing the film
web from the film web dispenser at a dispenser supply speed less
than the lowest demand speed at the applicator mandrel.
15. A process as claimed in claim 1, including stretching the film
web between the film web dispenser and the applicator mandrel.
16. A process as claimed in claim 1 including maintaining the film
web within a stress-strain variation range wherein film web stress
undergoes minimal variation while film web strain undergoes
comparatively greater variation throughout the revolution of the
film dispenser while the film web is positioned between the film
web dispenser and the applicator mandrel.
17. A process as claimed in claim 1, including prestretching the
film web in the film web dispenser at a sufficient pre-stretch
force and mechanical advantage so that it is beyond its pre-stretch
yield point, and subsequently further elongating the film web by
post-stretching the film web between the film web dispenser and
applicator mandrel beyond its post-stretch yield point at a
post-stretch force which is less than the pre-stretch force and
greater than the pre-stretch force reduced by the mechanical
advantage of the pre-stretch system.
18. A process as claimed in claim 17, including maintaining the
film web beyond its post-stretch yield point throughout the
revolution of the film dispenser while the film web is positioned
between the film web dispenser and the applicator mandrel.
19. A process as claimed in claim 1, including stretching the film
web beyond its yield point to plastically deform the film web
between the film web dispenser and the applicator mandrel.
20. A process as claimed in claim 1, including prestretching the
film web beyond its pre-stretch yield point to plastically deform
the film web in the film web dispenser, and subsequently
post-stretching the film web beyond its post-stretch yield point to
further plastically deform the film web between the film web
dispenser and the applicator mandrel.
21. A process as claimed in claim 19, wherein the stretching step
includes plastically deforming the film web throughout the
revolution of the film web dispenser.
22. A process as claimed in claim 20, wherein the post-stretching
step includes plastically deforming the film web between the film
web dispenser and the applicator mandrel throughout the revolution
of the film web dispenser.
23. A process as claimed in claim 20, including maintaining the
film web during the post-stretching step so that it is a force
lower than the force on the film web during the pre-stretching
step.
24. A process as claimed in claim 19, including maintaining the
film web beyond its yield point throughout the revolution of the
film web dispenser while the film web is between the film web
dispenser and the applicator mandrel.
25. A process as claimed in claim 20, including maintaining the
film web beyond its post-stretch yield point throughout the
revolution of the film web dispenser while the film web is
positioned between the film web dispenser and the applicator
mandrel.
26. A process as claimed in claim 19, including maintaining the
film web between the film web dispenser and the applicator mandrel
in the linear stress-strain range beyond the yield point throughout
the revolution of the film dispenser.
27. A process as claimed in claim 20, including maintaining the
film web between the film web dispenser and the applicator mandrel
in the linear stress-strain range beyond the post-stretch yield
point throughout the revolution of the film dispenser.
28. A process as claimed in claim 1, including positioning a bundle
having a plurality of bundle units in the applicator mandrel.
29. A process as claimed in claim 28, including positioning the
plurality of bundle units to form a bundle having as square a
cross-section as possible.
30. A process as claimed in claim 1 including wrapping a bundle of
a sufficiently small size that it can be grasped and carried by a
person and can constitute a unit of a pallet load.
31. A process as claimed in claim 1 including wrapping a bundle of
a sufficiently small size that its greatest cross-sectional
measurement is not substantially greater than two feet square.
32. A process as claimed in claim 1 including preventing the
application of substantial point loads to the film web from the
applicator mandrel and the bundle while dispensing the film web
onto the applicator mandrel.
33. A process as claimed in claim 1 including applying a
substantially uniform force across the full width of the film web
while dispensing the film web onto the applicator mandrel.
34. A process as claimed in claim 1 including positioning an oblong
cross-sectioned bundle having a wider side and a narrower side in
the applicator mandrel and supporting the film web on the
applicator mandrel so that the cross-section of the supported film
web is less oblong and more square than the bundle
cross-section.
35. A process as claimed in claim 1, wherein the recovering step
includes recovering the film web against opposed bundle sides
simultaneously.
36. A process as claimed in claim 1 including wrapping the film web
on an oblong cross-sectioned applicator mandrel to lock in
different forces on the film web on different sides of the
applicator mandrel and substantially reducing the difference
between locked in forces on the film web while applying the film
web from the applicator mandrel onto the bundle.
37. A process as claimed in claim 1, including applying at least a
portion of wrap force to said applicator mandrel.
38. A process as claimed in claim 1, including applying a wrap
force to the film web between the film web dispenser and the
application mandrel which if applied to the bundle would crush the
bundle, and applying a substantial portion of the wrap force to the
applicator mandrel to prevent the bundle from otherwise being
crushed during the dispensing step.
39. A process as claimed in claim 1 including preventing the film
web from being wrapped on the edges of the bundle by supporting the
film web on the applicator mandrel.
40. A process as claimed in claim 1 including applying a
sufficiently high wrap force to the film web between the film web
dispenser and the applicator mandrel, which if applied to the
bundle, absent the applicator mandrel, would dislodge the bundle
from its position, and applying a substantial portion of the wrap
force to the applicator mandrel to prevent the bundle from
otherwise being dislodged from its position during the dispensing
step.
41. A process as claimed in claim 1 including positioning a bundle
having a plurality of stacked units in the applicator mandrel
applying a sufficiently high wrap force to the film web between the
film web dispenser and the applicator mandrel, which if applied to
the bundle, absent the applicator mandrel, would dislodge at least
one of the stacked units from its position, and applying a
substantial portion of the wrap force to the applicator mandrel to
prevent the bundle units from otherwise being dislodged from their
positions during the dispensing step.
42. A process as claimed in claim 1, including positioning the
applicator mandrel to center each bundle on the revolution axis of
the film web dispenser.
43. A process as claimed in claim 1, including positioning the
bundle between at least two film web transporters on the applicator
mandrel.
44. A process as claimed in claim 43, including positioning the
widest surfaces of said bundle adjacent to film web transporters on
the applicator mandrel.
45. A process as claimed in claim 44, including supporting one of
the widest surfaces of the bundle on a horizontal conveyor and
transporting the film web with the film web transporters above the
top surface of the bundle and beneath the horizontal conveyor.
46. A process as claimed in claim 45, including positioning the
film web transporter adjacent the top surface of the bundle so that
it extends across the entire width of the top surface of said
bundle.
47. A process as claimed in claim 44, including positioning a
bundle having a plurality of bundle units stacked across the bundle
within the applicator mandrel and positioning the film web
transporter adjacent the top surface of the bundle so that it
extends across the top surface of the bundle at least to within
approximately one half of a bundle unit width of the lengthwise
topmost edges of said bundle.
48. A process as claimed in claim 44, including positioning the
film web transporter so that it extends across the top surface of
the bundle and so that the distance between the center of
revolution of the film web dispenser and the topmost lengthwise
edges of said film transporter is no greater than the distance from
the center of revolution of the film web dispenser and the topmost
lengthwise edges of said bundle.
49. A process as claimed in claim 44, including positioning the
widest surfaces of the bundle adjacent vertically positioned film
web transporters and on a conveyor beneath the bundle transporting
the bundle in a downstream direction.
50. A process as claimed in claim 49, including positioning a
bundle having a plurality of bundle units stacked to the height of
the bundle in the applicator mandrel and positioning film web
transporters adjacent opposed vertical sides of the bundle so that
they extend across opposed vertical sides of the bundle adjacent at
least the bottom half of the top most bundle units of the vertical
sides of the bundle.
51. A process as claimed in claim 1, including positioning an
oblong cross-sectional bundle having a wider side and a narrower
side in the applicator mandrel and supporting the film web on the
applicator mandrel at a greater distance away from the wider side
of the bundle than the narrower side of the bundle.
52. A process as claimed in claim 51, including supporting the
wider side of the bundle on a horizontal conveyor.
53. A process as claimed in claim 51, including supporting a
centered width of film web away from the wider side of the bundle,
the width of film web substantially equal to the width of the wider
side of the bundle.
54. A process as claimed in claim 51, including positioning a
bundle having a plurality of bundle units stacked across the wider
side of the bundle in the applicator mandrel and supporting a
centered width of film web away from the wider side of the bundle,
the width of film web approximately one bundle unit width less than
the width of the wider side of the bundle.
55. A process as claimed in claim 51, including supporting a
centered width of film web away from the wider side of the bundle
so that the distance between the center of revolution of the film
web dispenser and the edges of the width of film web is no greater
than the distance from the center of revolution of the film web
dispenser and the edges of the width of the bundle.
56. A process as claimed in claim 51, including supporting the
narrower side of the bundle on a horizontal conveyor running
through the applicator mandrel.
57. Process as claimed in claim 56, including positioning a bundle
having a plurality of units stacked to the height of the bundle in
the applicator mandrel and supporting a width of film web away from
the wider side of the bundle so that the top edge of the width is
approximately at least as high as the bottom half of the top most
bundle units.
58. A process for continuously stretch wrapping bundles of uniform
cross-section with film web dispensed from a film web dispenser
comprising:
moving the bundles into an applicator mandrel having a noncircular
cross-section;
dispensing a first film web in a first helical direction having a
first circular component and a second film web in a second helical
direction having a second circular component opposite to the first
circular component, the film web being dispensed from the film web
dispenser at a substantially constant supply speed by preventing
the supply speed of the film web at the film web dispenser from
decreasing and preventing the supply speed of the film web at the
film web dispenser from increasing;
stretching the film web in the direction in which it is
dispensed;
wrapping the stretched film web onto the applicator mandrel;
transporting the film web wrapped around the applicator mandrel
beyond the downstream end of the applicator mandrel;
continuing moving the bundle beyond the downstream end of the
applicator mandrel; and
applying the film web from the applicator mandrel onto the bundle
so as to provide a containment force in the film after it is
applied onto the bundle.
59. A process as claimed in claim 58 including applying a
sufficiently high wrap force to each of the two film webs between
the film web dispenser and the applicator mandrel, each of which,
if applied to the bundle, absent the applicator mandrel, would
spirally deform the bundle, and applying both film webs from the
applicator mandrel onto the bundle simultaneously to prevent spiral
deformation of the bundle.
60. A process for stretch wrapping a bundle with a film web
dispensed from a film web dispenser comprising:
moving the bundle into an applicator mandrel having a noncircular
cross-section;
revolving the film web dispenser relative to the applicator mandrel
at a rate of at least about 30 revolutions per minute;
dispensing the film web from the film dispenser at a substantially
constant supply speed by preventing the supply speed of the film
web at the film web dispenser from increasing and preventing the
supply speed of the film web at the film web dispenser from
decreasing, wrapping the stretched film web onto the applicator
mandrel, restraining and retarding the film web being dispensed by
the film dispenser, the dispenser supply speed being less than the
lowest demand speed at the applicator mandrel, stretching the film
web beyond its yield point to plastically deform the film web
between the film web dispenser and the applicator mandrel
throughout the revolution if the film dispenser, and maintaining
the film web between the film web dispenser and the applicator
mandrel in the linear stress-strain range throughout the revolution
of the film web dispenser;
transporting the film web wrapped around the applicator mandrel
beyond the downstream end of the applicator mandrel;
continuing moving the bundle beyond the downstream end of the
applicator mandrel; and
applying the film web from the applicator mandrel onto the bundle
so as to provide a containment force in the film web after it has
been applied onto the bundle.
61. A process as claimed in claim 60, including substantially
pre-stretching the film web in the film dispenser prior to
dispensing the film web.
62. A process for stretch wrapping a bundle with a film web
dispensed from a film web dispenser comprising:
moving the bundle into an applicator mandrel having a noncircular
cross-section;
revolving the film web dispenser relative to the applicator
mandrel;
substantially pre-stretching the film web in the film web dispenser
prior to dispensing the film web;
dispensing the film web from the film web dispenser at a
substantially constant supply speed by preventing the supply speed
of the film web at the film web dispenser from increasing and
preventing the supply speed of the film web at the film web
dispenser from decreasing;
wrapping the stretched film web onto the applicator mandrel;
restraining and retarding the film web being dispensed by the film
web dispenser;
transporting the film web wrapped around the applicator mandrel
beyond the downstream end of the applicator mandrel;
continuing moving the bundle beyond the downstream end of the
applicator mandrel; and
applying the film web from the applicator mandrel onto the bundle
so as to provide a containment force in the film web after it is
applied onto the bundle.
63. A process as claimed in claim 62, including dispensing the film
web from the film web dispenser at a supply speed less than the
lowest demand speed at the applicator mandrel.
64. A process as claimed in claim 62, including stretching the film
web beyond its yield point to plastically deform the film web
between the film web dispenser and the applicator mandrel.
65. A process as claimed in claim 62, including prestretching the
film web beyond its pre-stretch yield point to plastically deform
the film web in the film web dispenser, and subsequently
post-stretching the film web beyond its post-stretch yield point to
further plastically deform the film web between the film web
dispenser and the applicator mandrel.
66. A process as claimed in claim 63, where the post-stretching
step includes plastically deforming the film web between the film
web dispenser and the applicator mandrel throughout the revolution
of the film web dispenser.
67. A process as claimed in claim 64, including maintaining the
film web between the film web dispenser and the applicator mandrel
in the linear stress-strain range beyond the post-stretch yield
point throughout the revolution of the film dispenser.
68. A process as claimed in claim 65, including maintaining the
film web between the film web dispenser and the applicator mandrel
in the linear stress-strain range beyond the post-stretch yield
point throughout the revolution of the film dispenser.
69. A process for stretch wrapping a bundle with a film web
dispensed from a film web dispenser comprising:
moving the bundle into an applicator mandrel having a noncircular
cross-section;
revolving the film web dispenser relative to the applicator
mandrel;
dispensing the film web from the film web dispenser at a
substantially constant supply speed by preventing the supply speed
of the film web at the film web dispenser from increasing and
preventing the supply speed of the film web at the film web
dispenser from decreasing;
stretching the film web and wrapping the film web onto the
applicator mandrel while plastically deforming the film web between
the film web dispenser and the applicator mandrel throughout the
revolution of the film web dispenser;
transporting the film web wrapped around the applicator mandrel
beyond the downstream end of the applicator mandrel;
continuing moving the bundle beyond the downstream end of the
applicator mandrel; and
applying the film web from the applicator mandrel onto the bundle
so as to provide a containment force in the film web after it is
applied onto the bundle.
70. A process as claimed in claim 69, including maintaining the
film web between the film web dispenser and the applicator mandrel
in the linear stress-strain range throughout the revolution of the
film web dispenser.
Description
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to a process for wrapping bundles
with stretched film web and more particularly, a process of
unitizing a bundle having a plurality of bundle units at extremely
high throughput rates with high film web elongation and containment
force on the bundles.
II. Description of the Related Art
It has become popular to package products into bundles by wrapping
the products with a web of stretched plastic film. The elasticity
of the stretched plastic film holds the products of the bundle
under tension while unitizing and covering the bundle.
For a film web wrapping process to be commercially competitive, it
has been increasingly necessary to wrap bundles at a very high
throughput. This is especially true for business enterprises which
need to wrap large numbers of bundles having a uniform
cross-sectional shape. The conventional cross-sectional shape is
rectangular in order to economize shipping space and facilitate
stacking. Due to corner variations which change the effective
wrapping radius, bundles having such rectangular cross-sections or
other non-circular cross-sections, present a fluctuation in its
demand for film web as the film web is wrapped around its
periphery.
General Background to Problems With Varying Demand Rates During
Wrapping
FIGS. 10-12 show the fluctuation in film demand due to bundle shape
variations such as corners. A bundle 40 is centered on axis Y. A
film web dispenser 70 is revolved around axis Y at a constant
angular velocity and at a constant distance from axis Y to wrap
film web 58, moving in direction D around stationary bundle 40. The
effective wrapping radius increases from A to B during the
progression between FIGS. 10 and 11 and decreases to radius C
between FIGS. 11 and 12. The effective wrapping radii A, B, and C
extend between center of revolution Y and tangent T, and if
rotated, form circles J, K, and L, respectively.
Under constant angular velocity of film web dispenser 70, the film
web demand rate is proportional to the effective wrapping radius.
FIG. 10 shows a minimum demand rate where the wider side of an
oblong bundle has just been wrapped. FIG. 11 shows a maximum demand
rate where the film engages a corner. FIG. 12 shows a secondary
minimum demand rate where the narrower side of an oblong bundle has
just been wrapped. This secondary minimum demand rate is less than
the maximum demand rate shown in FIG. 11, but greater than the
minimum demand rate shown in FIG. 10 because effective radius C is
greater than effective radius A due to the oblong shape of the
bundle.
The relation between demand rate or speed and time is shown in FIG.
5. The maximum demand rate or speed existing at the corners in the
condition shown in FIG. 11 is indicated by maximum points 154 in
FIG. 5. Minimum demand rates or speeds in the positions shown in
FIGS. 10 and 12 are indicated by minimum points 152 in FIG. 5.
If film web 58 is dispensed from film web dispenser 70 at a
constant supply rate such as that shown in FIG. 6, the film web
stretched between film web dispenser 70 and bundle 40 would follow
a pattern of elongation over time that would be similar to the
pattern of the demand rate over time. Such a pattern of elongation
over time is shown in FIG. 7. This elongation pattern of FIG. 7 is
similar to the demand rate pattern shown in FIG. 5. Elongation
maximums 144 correspond to demand rate maximums 154. Elongation
minimums 142 correspond to demand rate minimums 152.
During wrapping, bundle edges isolate tension on each film web
segment applied to a bundle surface from film web segments applied
to adjacent surfaces. The effective containment force on the bundle
is locked in just as it covers a bundle surface in the positions
shown in FIGS. 10 and 12. Therefore, the locking in of containment
force occurs where the demand rate and force on the film is lowest
in the wrapping cycle.
It can be appreciated that in the arrangement shown in FIGS. 10-12,
when the bundle is off-center relative to rotation axis Y, the
demand rate and wrap forces would fluctuate even more widely
between a maximum and a minimum for each side of the bundle due to
greater variations in the effective wrapping radius.
Within the context of this varying demand rate due to bundles with
a non-circular cross-section, efforts were made to control the rate
at which the film web is dispensed from the film web dispenser to
provide a sufficient containment force due to stressed film web on
the wrapped bundle while preventing film rupture at excessively
high stresses. A varying film web demand rate creates the adverse
situation that the film stress-strain maximum must not rupture the
film, while the stress-strain minimum is the containment force
locked in after wrapping. In order to have any containment force,
the minimum must exceed zero stress.
Demand Force Controlled Supply Rate Systems
At slow film web supply rates, the force on the film web between
the film web dispenser and the bundle generally proportional to the
varying demand rate. Therefore, early film web dispensers
controlled the supply rate of the film web by measuring the force
on the film web. Then they varied the film web supply rate of the
dispenser accordingly so that the supply rate of the film web from
the dispenser followed the demand rate for the film web caused by
the corner variations of the bundle. By maintaining a constant
force on the film web, the stress-strain values for the film web
could be kept constant over time and therefore maintain a high
containment force while preventing an increase in force due to
fluctuations in demand rate which would rupture the film. The
demand, supply, and force curves of this control arrangement are
seen in FIGS. 23, 24 and 25.
However, there are major drawbacks in controlling film web
dispenser supply rates by the sensing of variations in force on a
film web due to the varying demand rate of a non-circular
cross-sectioned bundle. The first drawback is that any imperfection
such as a hole in the film web reduces the area over which the
force is applied. This dramatically increases the stress on the
remaining cross-sectional area of the film web. The hole is further
elongated and enlarged because the control system automatically
decreases the supply speed at the dispenser. This growing
difference between the supply and demand speeds finally ruptures
the film.
The second drawback occurs when the film web is dispensed at higher
speeds in an attempt to increase throughput. The inertia of the
film dispenser and the elasticity of the film web between the film
web dispenser and the bundle cause a phase delay or lag in supply
speed changes relative to demand speed changes. This phase delay
has its worst drawbacks when the supply rate lags the demand rate
such that the supply rate is increasing while the demand rate is
decreasing and the supply rate is decreasing while the demand rate
is increasing. Rather than equalizing the force on the film over
time due to the variations in demand rate, such a phase delay
causes a heightened variation in force and elongation on the film
web, thereby rupturing the film web.
Speed Controlled Supply Rate Systems
A second type of control for varying the supply rate of the film
dispenser due to the variations in demand rate was developed in
order to overcome the drawbacks of the force controlled dispensing
system. This system, rather than sensing force in the web, was
designed to vary the supply rate of the film web according to the
known supply rate which would be required to meet the instantaneous
demand rate at each position of the film web dispenser's revolution
about the bundle. By not sensing force, the film web was not
ruptured due to the drawbacks caused by its imperfections. In
addition, phase delay drawbacks were avoided at somewhat higher
speeds. However, as the speed of the film web dispenser was further
increased, an inordinate amount of power was required in order to
more quickly accelerate and deaccelerate the film web supplied from
the film web dispenser. Therefore, film web dispensers which
controlled supply rate according to dispenser position were unable
to attain high film web supply speeds as well.
Stress-Strain Characteristics of Film Webs
As shown in FIG. 8, film webs exhibit a stress-strain curve having
a steep initial linear portion 140E where elastic behavior is
present and a gradual second linear portion 140P where plastic
behavior is present. In between these two linear ranges is an
intermediate range or region on the stress-strain curve commonly
known as the yield point 141. It is in the range of this yield
point that the stress-strain behavior of the film web changes
between substantially elastic to plastic. Film webs stretched above
yield point gain significantly in modulus and ultimate strength.
For instance, a low density polyethylene film web will increase its
ultimate strength in pounds per square inch of cross-sectional area
by 300% after being elongated approximately 300%. Therefore,
current stretch wrapping operations use prestretch subsystems in
the film web dispenser as a matter of course.
Stress-strain curves are dependent upon the end conditions of the
film web and the previous history of stress and strain in the film
web. For example, in the arrangement shown in FIG. 10, the
stress-strain curve of the film web between closely spaced rollers
a and b in the pre-stretch subsystem of the film web dispenser 70
is different although generally similar in shape to the
stress-strain curve of the film web between the more greatly spaced
downstream roller b and bundle 40.
If an unstretched film web is stretched from the point of origin 0
along the elastic portion 140E of the stress-strain curve to a
point no further than yield point 141, the film web will return to
a stress-strain condition along the same curve 140E when the
stretch force is reduced or removed, and will once again have zero
strain at zero force.
However, if the film web is stretched beyond yield point 141 so
that it reaches a point on the plastic portion 140P of the curve
such as point 148, the film web behavior after the force is reduced
or removed will be to progress down curve 150 rather than returning
back along curve 140P and 140E. If the force is now totally
removed, the film web will exhibit a permanent positive elongation
indicated by point 160.
Prestretch Devices
In seeking to decrease the amount of film web needed for a given
containment force, pre-stretch devices were developed to
pre-stretch the film web in the film web dispenser under controlled
conditions between closely-spaced rollers which rotated at a
constant ratio. Such pre-stretching produced a permanently
elongated film with good strength characteristics. As shown in FIG.
10, film web dispenser 70 includes a pre-stretch system having
upstream roller a and downstream roller b which isolate the film
web from the demand rate variances generated by the bundle.
Upstream roller a is conventionally connected to downstream roller
b by a constant ratio gear train with a mechanical advantage which
causes downstream roller b to rotate faster than upstream roller a
and thereby stretch the film web between rollers a and b.
However, conventional attempts to increase the force on the film
between the film web dispenser and the bundle resulted in breaking
the film web. Therefore, in order to avoid rupturing the film web
after pre-stretching it in the film web dispenser, it has been
conventional to supply the film web from the dispenser to the
bundle at a supply rate greater than the maximum demand rate at the
bundle so that the film web recovers or reduces its elongation to a
value less than the elongation provided by the pre-stretch device
in the supply direction. In addition, the wrap force, or force on
the film web between the film web dispenser and the bundle, is
conventionally maintained at a value less than the pre-stretch
force, or force on the film web between the rollers in the
pre-stretch device of the film web dispenser. Under such
conditions, the film web would elastically recover to a point along
recovery curve 150 after being pre-stretched to point 148.
Therefore, the wrap force on the film web between the film web
dispenser and the bundle conventionally varied between a minimum
142 and a maximum 143 on recovery curve 150 due to fluctuation in
demand rate caused by a non-circular bundle.
In order to keep the film web between the film web dispenser and
the bundle at a stress-strain condition along recovery curve 150, a
number of systems have been developed which use a motor which
supplied a positive torque to downstream roller b of the
pre-stretch device. The motor had the effect of driving the film
forward from the film web dispenser. Such motors and their control
systems have had the capability of controlling the minimum film web
supply speed by increasing supply speed if it were to fall below a
predetermined minimum supply rate. However, they have not had the
capability of controlling the maximum film web supply speed because
it was not thought to be necessary. With such motors and control
systems, if high supply speeds were attempted, the motors would be
driven by the film faster than their set maximum constant supply
speed. This set up an overrun condition, described below, which
destroyed the film web.
Therefore, even though the pre-stretch approach achieved more
precise and effective elongation performance than rudimentary
braking devices which were originally used to stretch the film, and
although greater film web economies and improved containment
reliability was increased by reducing high forces to the bundle,
the throughput and usefulness of the pre-stretch approach has also
been limited by the variation and forces caused by the contours of
a non-circular bundle cross-section.
Film Speed Limited: Drawbacks of Other Conventional Demand Force
Controlled Supply Rate Systems
U.S. Pat. Nos. 4,302,920 and 4,317,322 disclose prestretch
dispensers in which changes in the demand rate due to corner
variations of a non-circular load are transmitted directly through
the film to the dispenser to vary the dispenser supply rate
according to the bundle demand rate. U.S. Pat. Nos. 4,387,548,
4,387,552 and 4,524,568 disclose the use of constant positive
torque supply motors which drive the film web forward to reduce the
force and elongation on the film web between the dispenser and the
bundle after it has been pre-stretched. U.S. Pat. Nos. 4,503,658
and 4,514,955 disclose the use of varying positive torque supply
motors which drive the film web forward to reduce and unify over
time the force and elongation on the film web between the dispenser
and the bundle after it has been prestretched. However, all these
systems are inoperable at high speed throughput such as film web
dispenser angular orbit velocities above around 25 revolutions per
minute. This limitation is due to the drawbacks of demand force
controlled supply systems including destruction of film web due to
imperfections and phase shift effects.
Film Force Limited: Drawbacks of Other Conventional Speed
Controlled Supply Rate Systems
U.S. Pat. No. 4,418,510 discloses the use of a constant positive
speed control motor which drives the downstream roller of the film
dispenser at a supply rate in excess of the demand rate for the
film by the bundle. This system avoids the drawbacks of the force
demand controlled supply systems of web hole expansion and phase
lag. However, if the film web were stretched at a sufficiently high
force and elongation rate, the motor, rather than positively
driving the film web forward, would need to restrain the film web.
Since no provision exists in conventional motor system and their
control systems to prevent the motor from exceeding its set
predetermined supply speed, if it is so drawn by the film web, the
internal inertia and friction of the motor would be acting in an
uncontrolled way as a brake on the film web.
Rather than driving the film web forward, the motor supply speed
would be overrun by a film web speed that was faster than the set
constant supply speed of the motor. The motor would be driven by
the tension in the film web between the dispenser and the bundle in
a demand force controlled way which varies the supply speed of the
dispenser in response to varying the demand speed of the
bundle.
In effect, the control of the dispenser supply rate would be
converted to a demand force controlled supply rate system with the
attendant problems of such systems, namely destruction of film web
due to imperfections and phase lag which prevent operation at high
throughput speeds.
Such overrunning of the positive speed supply motor would occur at
stress-strain conditions above yield point of the film web between
the dispenser and the bundle. Therefore, this would prevent a
conventional system from operating at such stress-strain conditions
above yield point.
One can tell when the motor is being driven by the film web rather
than driving the film web as intended by convention systems by
analyzing whether a system is being overrun.
If higher than conventional wrap forces were attempted in a
positive torque supply motor control pre-stretch system, the film
web alone would drive the rollers of the pre-stretch system and the
positive torque motor would be driven by the pre-stretch system at
speeds higher and more varying than the intended motor speed. The
film web overdrives the motor and causes it to act in an
uncontrolled way as a brake when the wrap force F.sub.2, between
the film web dispenser and the bundle, is related to the prestretch
force F.sub.1 between the pre-stretch rollers according to the
following relationship:
where R.sub.S is the radius of the downstream roller gear and RL is
the radius of the upstream roller gear. In order to have
prestretch, R.sub.S is always less than R.sub.L so that the term
(1-R.sub.S /R.sub.L) is always positive and less than 1, and an
overrun force F.sub.2 is less than F.sub.1. For example, if R.sub.S
/R.sub.L =1/3, a conventional value, then F.sub.2 equals 2/3*
F.sub.1 when overrun occurs.
In summary, when overrun occurs, the supply rate of the film web
from the film web dispenser is dependent on the force of the film
web between the film web dispenser and the bundle. Such a system
suffers from the drawbacks of force controlled dispensers discussed
above, namely, rupture of films with imperfections and problems
with phase lag which prevent high throughput operation.
Film Force Limited: By Grossness of Load and Point Force From
Load
The Kaufman Company Stretch Command III pre-stretch pallet load
wrapping system also used a constant positive speed control motor
on the film web dispenser. Although the pallet was rotated at a
constant angular velocity, corner variations caused a varying
demand rate which varied over a very wide range due to the great
size of the pallet. The film web supply speed and force on the film
web had to be limited to a narrow range to avoid crushing the
pallet load or losing containment from some sides of the pallet
load. Therefore, high wrap forces are impossible.
Also, the corners of the pallet load and the corners of the
individual units making up of the pallet load, when wrapped with
the film web would create a point force loads, on the film web
which cause rupture of the film web at high film web wrap
forces.
Finally the Kaufman motor would suffer the same overrun problems,
discussed above, if high wrap forces could otherwise be attained
despite the grossness in load problems. Such overrun problems would
have occurred if the supply speed was substantially lower than the
highest demand rate.
The Anderson Company pallet wrapper, introduced at the 1978 Chicago
PMMI Show and illustrated as prior art in U.S. Pat. No. 4,503,658,
interconnected the film web supply with the pallet turntable with a
variable transmission. Constant film web supply speed could be
attained and no demand force controlled overrun problems would
occur. However, the grossness of load and point source load
problems prevented speed and force operation outside the same range
as Kaufman. Even if these problems could be overcome, high wrap
forces would prevent an effective operation by dislodging the
pallet load from its position.
Film Force Requirements: Use of Conveyors and Other Bundle
Supports
Conveyors and other bundle supports have been used in bundle
wrapping in order to transport and support the bundle during
wrapping. An example of such a system is shown in U.S. Pat. No.
4,317,322. However, conveyors and other bundle supports increased
the cross-sectional wrapping area since they were positioned on the
outside of the bundle. When using conveyors and other supports, the
film web would have to additionally recover against the bundle
after the bundle had been moved off of the conveyor because of the
cross-sectional area of the bundle relative to the conveyor and the
supports.
The film force limitations of the conventional systems discussed
above are even more critically limiting when used with conveyors
and other bundle supports. This is because even greater force on
the film web is required to wrap the bundle on the conveyor and
support so that adequate containment force would be available
subsequent to film web recovery onto the bundle from the conveyor
and bundle supports after the bundle had been removed from the
conveyor and supports after wrapping. However, in order to avoid
bundle collapse during wrapping, the force to the bundle
conventionally was minimized and the recovery of film against the
bundle produced a substantially reduced containment force.
Film Force Limited: Problems With Multiple Unit Bundles
Multiple unit bundles consist of a number of individual units, with
each unit being a box or carton such as one which is ultimately
delivered to the consumer. The units may be stacked both across the
width, length, and height of the bundle. Such bundles of individual
units have practically no internal structural strength since the
friction between the units is minimized by their shape, mass and
container surface characteristics. Therefore, it has been
significantly difficult to wrap a bundle of these individual units
with a film web at a wrap force which is sufficiently high to
result in a containment force on the bundles while not skewing the
bundles either during or after the wrapping process. However,
multiple unit bundles also have a special requirement for a
containment force which is high enough to form a tight bull's-eye
pattern in the film at the ends of the bundle. A tight bull's-eye
means smallness of size of the aperture defined by the film ends on
the ends of the bundle after wrapping, and tightness on the film
web on the bundle ends. Although this is desirable on any wrapped
bundle, it is especially desirable and necessary on bundles having
multiple units to prevent the units from falling out of the
bull's-eye or shifting.
Film Force Limited: Problems With Crushing
The regulation of wrap force has also been a problem with fragile
crushable bundles. Since only the minimum force is locked into the
wrapped film web due to the varying demand rate of a non-circular
cross-sectioned bundle, such bundles must be wrapped with a
sufficiently high wrap force in order to have a sufficiently high
containment force. However, the wrap force also needs to be
sufficiently low such that the packages will not be crushed. The
result of this situation is that crushable bundles conventionally
are often crushed during wrapping or are wrapped in film web which
provides insufficient containment force.
Film Force Limited: Problems With Bundles Having Oblong
Cross-Sections
There is a further aggravating factor in conventional film wrapping
systems which reduces containment forces on bundles having oblong
cross-sections. A film web segment applied to any side of a bundle
exhibits elongation and force independent of the contiguous film
web applied to either of the surfaces wrapped immediately prior to
or after the given side. This is because bundle edges isolate
tension on each film web segment applied to a surface from
connecting film web segments applied to adjacent surfaces. Since
slippage and tension equalization across edges does not occur,
extreme tension differences exist between the consecutive segments
of a wrapped bundle having an oblong cross-section. Further, since
the locking in of forces occurred where the film web had recovered
to a minimum elongation, only the minimum containment
characteristics are locked into the film web.
Summary
In summary, conventional wrapping systems suffer from many
drawbacks.
It has been difficult to obtain a high throughput speed, high film
dispenser orbit speed and high film dispensing speeds due to
difficulties in controlling supply of the film web from the film
web dispenser.
It has been difficult to prevent film rupture due to the grossness
of load, point source loading due to corners of a bundle, and
uncontrolled high stresses due to uncontrolled operation of
pre-stretch systems due to overrun.
It also has been difficult to obtain high containment forces on the
wrapped bundle due to the use of conveyors and other supports for
the bundle due to recovery of pre-stretch elongation which occurred
between the film web dispenser and the bundle during wrapping.
It has been further difficult to obtain high containment forces on
the wrapped bundle because of the difficulties in properly
positioning and orienting of the bundle relative to the wrapping
system.
It has been difficult to prevent the bundle and subunits of the
bundle from being dislodged from the wrapping position due to the
high wrapping force on the film web which is required to produce an
adequate containment force on the bundle.
It has been difficult to prevent crushing of the bundle during
wrapping due to the wrapping force required in the film web to
produce an adequate containment force on the bundle.
It has been difficult to prevent great changes in stress on the
film dispenser and film web during wrapping due to varying demand
rates caused by film web demand variations in a non-circular
cross-sectioned bundle.
It has been difficult to obtain a high wrap force due to bundle
sensitivity and difficulties in controlling film supply.
It has been difficult to obtain high elongation of the film web
during wrapping for efficient use of the film web while obtaining
high containment forces without rupturing the film.
It has been difficult to equalize locked-in forces in the film web
when wrapping oblong bundles.
It has been difficult to apply wide film web while minimizing
wrinkles in the film web after it has been applied to the
bundle.
It has been difficult to obtain, due to lack of adequate
containment force, a tight bull's-eye pattern in the film at the
ends of the bundle.
In view of these difficulties with conventional systems there are a
variety of objects which the present invention seeks to
achieve.
It is a further object of the present invention to obtain a high
throughput speed, high film dispenser orbit speed, and high film
dispensing speeds by effectively controlling supply of the film web
from the film web dispenser while providing high film web
containment force on the bundle after wrapping.
It is an object of the present invention to prevent film rupture
due to the grossness of load, point source loading due to corners
of a bundle, and uncontrolled high stresses due to uncontrolled
operation of pre-stretch systems due to overrun.
It is an object of the present invention to obtain high containment
forces on the bundle while using conveyors and other supports for
the bundle.
It is another object of the present invention to obtain high
containment forces by properly positioning and orienting of the
bundle relative to the wrapping system.
It is also an object of the present invention to prevent the bundle
and subunits of the bundle from being dislodged from the wrapping
position due to high wrapping force on the film web which is
required to produce adequate containment force on the bundle.
It is a further object of the present invention to prevent crushing
of the bundle during wrapping due to the wrapping force in the film
web which is required to produce an adequate containment force on
the bundle.
It is another object of the present invention to prevent great
changes in stress on the film dispenser and film web during
wrapping due to varying demand rates caused by film web demand
variations in a non-circular cross-sectioned bundle.
It is an additional object of the present invention to obtain a
high wrap force due to bundle sensitivity and difficulties in
controlling film supply.
It is also an object of the present invention to obtain high
elongation of the film during wrapping for efficient use of the
film web while obtaining high containment forces without rupturing
the film.
It is also an object of the present invention to equalize locked in
forces in the film web when wrapping oblong bundles.
It is an additional object of the present invention to apply wide
film web while minimizing wrinkles in the film web after it has
been applied to the bundle.
It is another object of the present invention to obtain a tight
bull's-eye pattern in the film at the ends of the bundle.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
To achieve the foregoing objects, and in accordance with the
purposes of the invention as embodied and broadly described herein,
there is provided a process for wrapping a bundle with a film web
dispensed from a film web dispenser comprising moving a bundle into
an applicator mandrel, revolving the film web dispenser relative to
the applicator mandrel, dispensing the film web from the film web
dispenser onto the applicator mandrel at a constant supply speed,
transporting the film web wrapped around the applicator mandrel
beyond the downstream end of the applicator mandrel, continuously
moving the bundle beyond the downstream end into the applicator
mandrel, and applying the film web from the applicator mandrel onto
the bundle so as to provide a containment force in the film web
after it is applied onto the bundle.
It is preferable to restrain and retard the film web being
dispensed by the film web dispenser. It is also preferable to
dispense the film web from the film dispenser at a dispenser supply
speed less than the lowest demand speed at the applicator
mandrel.
It is pre-stretch the film web beyond its pre-stretch yield point
to plastically deform the film web in a film dispenser and
subsequently post-stretch the film web in the linear stress-strain
range beyond its post-stretch yield point to plastically deform the
film web between the film web dispenser and the applicator mandrel
throughout the revolution of the film web dispenser.
It is preferable to position an oblong cross-sectioned bundle
having a wider side and a narrower side in the applicator mandrel
and supporting the film web on the applicator mandrel so that the
cross-section of the supported film web is less oblong and more
square than the bundled cross-section.
It is preferable to prevent the application of substantial point
loads to the film web from the applicator mandrel and supply a
substantially uniform force across the full web width of the film
web while dispensing the film web onto the applicator mandrel.
It is preferable to maintain the film web within a stress-train
variation range wherein film web stress undergoes minimal variation
while film web strain undergoes comparatively greater variation
throughout the revolution of the film web dispenser while the film
web is positioned between the film web dispenser and the applicator
mandrel.
It is preferable to dispense a first film web in a first helical
direction having a first circular component and a second film web
on a second helical direction having a second circular component
opposite to the first circular component.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate a preferred embodiment of
the invention and, together with the general description given
above and the detailed description of the preferred embodiment
given below, serve to explain the principles of the invention.
FIG. 1 is a perspective view of a dual-stage wrapping apparatus
capable of performing the process of the present invention;
FIG. 2 is a side view of the apparatus of FIG. 1;
FIG. 3 is a front cutaway view taken along line 3--3' of FIG.
2;
FIG. 4 is a rear cutaway view taken along line 4--4' of FIG. 3;
FIG. 5 is a graph of demand for film web at a wrapped rectangular
applicator mandrel of the present invention;
FIG. 6 is a graph of film web supply from the dispenser of the
present invention;
FIG. 7 is a graph of film web elongation exerted between the
dispenser and the applicator mandrel of the present invention;
based on the demand shown in FIG. 5 and the supply shown in FIG.
6;
FIG. 8 is a graph illustrating the relationship of force and
elongation in conventional wrapping processes;
FIG. 9 is a schematic view of a conventional wrapping conveyor and
bundle;
FIG. 10 is a schematic view of a prior art dispenser and bundle,
illustrating a point of minimum demand for film web at the
bundle;
FIG. 11 is the schematic view of the bundle and dispenser at FIG.
10 at a later point in time, illustrating a point of maximum demand
for,film web at the bundle;
FIG. 12 is a schematic view of a dispenser apparatus and bundle of
FIG. 11 at a later point in time, illustrating a point of secondary
minimum demand for film web at the bundle;
FIG. 13 is an isolated side view of an elongation mechanism of the
apparatus of FIG. 3;
FIG. 14 is a graph illustrating the relationship of stress and
strain on the film web when pre-stretched in the film web dispenser
and stretched again at the applicator mandrel of the present
invention;
FIG. 15 is a graph illustrating the relationship of stress and
strain on film web stretched between the dispenser and the
applicator mandrel of the present invention;
FIG. 16 is a schematic view of a bundle and an applicator mandrel
spanning the full width of widest bundle surfaces;
FIG. 17 is a schematic view of a bundle and an applicator mandrel
spanning a portion of the width of opposed widest bundle
surfaces;
FIG. 18 is a schematic side view illustrating severance of
continuously wrapped bundles;
FIG. 19 is an isolated side view, upstream from the first wrapping
stage, of an applicator mandrel configured for tall bundle
contours;
FIG. 20 is an isolated side view, downstream from the second
wrapping stage, of the applicator mandrel of FIG. 19;
FIG. 21 is a front view of the applicator mandrel of FIG. 19;
FIG. 22 is an isolated perspective view of a transmission for the
wrapping conveyor of FIG. 2.
FIG. 23 is a graph of demand for film web;
FIG. 24 is a graph of film web supply from the dispenser;
FIG. 25 is a graph of film web elongation under the demand shown in
FIG. 23 and the supply shown in FIG. 24; and
FIG. 26 is a diagram of a motor speed controller with regenerative
capabilities which are arranged according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the present preferred
embodiment of the invention as illustrated in the accompanying
drawings.
The wrapping process of the present invention will be described as
being performed on the dual-dispenser apparatus and also shown in
FIGS. 1-4 described in copending application Ser. No. 582,779.
As shown in FIG. 2, a plurality of units 43 forming bundles 40 have
been loaded in stacked relationship on an infeed conveyor assembly
31 either manually or mechanically. As an alternative to the
conveyer, descending freewheel rollers or a pneumatic or hydraulic
pushing device can be used to engage and push each bundle 40 into
the wrapping area.
An upstream wrapping stage 35 and a downstream wrapping stage 36
are mounted to frame 38. Each wrapping stage includes a dispenser
barrel 50 for revolving a film roll 56 and a film web dispenser
around a bundle 40. The film web dispenser includes elongation
mechanism 70. The dispenser barrel 50 includes a mounted hoop 52, a
free hoop 54, and a plurality of barrel tubes 53 joining hoops 52
and 54 so that they are coaxial and parallel to one another.
As shown in FIG. 3, mounted hoop 52 is bolted or otherwise fixed
coaxially to the outermost race 44 of a circular triple bearing
race 42. The middle bearing race 46 of a triple race 42 is fixed to
the frame 38, and the innermost race 48 is freely driven to rotate
for purposes which will be described below. A dispenser motor 60 is
mounted to the frame and coupled through right angle reducer 61 to
drive friction wheel 62 which is in contact with outer race 44.
Thus, operation of motor 60 will rotate friction wheel 62, outer
race 44 and dispenser barrel 50.
Elongation motor 64 is coupled through reducer 65 to reducer pulley
63. A belt 59 surrounds pulley 63, tension pulley 66, and drive
pulley 67. Drive pulley 67 is mounted on shaft 68 which in turn is
mounted to the frame 38 and extends inside the inner race 48. As
shown in FIG. 4, friction roller 69 contacts inner race 48 and is
mounted to shaft 68. Therefore, operation of motor 64 will drive
the belt 59, the pulley 67, friction roller 69 and inner race
48.
The film web dispenser elongation mechanism 70 and film roll 56 are
mounted on the dispenser barrel 50 opposite a counterweight 90. The
elongation mechanism 70 includes an upstream roller 72 and
downstream roller 74 which are driven by elongation motor 64 to
rotate at respective fixed constant surface speeds. Film web 58 is
drawn from roll 56 across the surface of the upstream roller 72
rotating at a first constant speed and then across the surface of
the downstream roller 74 rotating at a second constant speed higher
than the first constant speed. The film web 58 is stretched between
the upstream and downstream rollers 72 and 74 at a constant stretch
ratio corresponding to the ratio of the speeds of the upstream and
downstream rollers 72 and 74. For film webs which are currently
popular, the stretch ratio is preferably in the range of 1:2 to
1:3.
As shown in FIG. 2, core hubs 91 and 92 are mounted adjacent to
each of the hoops 52 and 54 to engage the hollow core of film roll
56 and maintain film roll 56 rotatably mounted on the dispenser
barrel 50. Core hub 92 and disk brake 94 are pivotally mounted to
the hoop 52 by hinge 96. Brake 94 engages the hub 92 and restrains
the hub 92 from free rotation. This prevents rapid spillage of film
web 58 from film roll 56 during shutdown of the wrapping operation.
Brake 94 also prevents slack on the web between roller 56 and
roller 72 as film payout reduces the diameter of film roll 56.
As shown in FIG. 4, core hub 91 is mounted to swing plate 93 which
pivots across the plane of hoop 54 on pivot shaft 95 journalled to
hoop 54. At an end of swing plate 93 opposite shaft 95, a locking
pin 97 is removably engaged with hoop 54. It may be engaged by
spring pressure to enter a blind bore of hoop 54, or by being
threaded to a threaded bore of hoop 54. Handle 98 is coupled to pin
97 for manual release of pin 97 from the hoop 54 when film roll 56
is completely dispensed. Plate 93 and core hub 91 may then be swung
away from the roll core about shaft 95, and the core may be tilted
outward from the hoop 54 on the hinge 96, shown in FIG. 2. The roll
core then may be removed easily by hand and a fresh film roll 56
may be mounted by engaging one end of the roll core to hub 92,
swinging the roll inward, and closing swing plate 93 to engage hub
91 with the core of the roll 56. Pin 97 then is locked into the
hoop 54 to maintain new film roll 56 in place.
As shown in FIG. 13, upstream roller 72 is mounted on upstream
shaft 73 one end of upstream shaft 73 is journalled to support
plate 79 on hoop 54. The other end of upstream shaft 73 passes into
a transmission housing 71. Downstream roller 74 is mounted on
downstream shaft 75. One end of downstream roller 74 is journalled
to plate 79 and the other end passes through the transmission
housing 71. An upstream gear 76 is mounted to upstream shaft 73 in
housing 71. A downstream gear 78, smaller than upstream gear 76, is
mounted to downstream shaft 75 and is coplanar with upstream gear
76. The ratio of gears 76 and 78 preferably is in the range of 2:1
to 3:1. Additionally, a tension shaft 88 is journalled within
transmission housing 71 and a tension gear 87 is mounted to shaft
88 coplanar with gears 76 and 78 so that a chain surrounding gears
76, 78 and 87 will follow a triangular path. A transmission chain
77 encompasses gears 76, 78, and 87 to define a fixed speed ratio
between gears 76 and 78, shafts 73 and 75, and upstream roller 72
and downstream roller 74.
Downstream drive gear 86 is mounted to downstream shaft 75 in
transmission housing 71. A shaft bracket 81 is fixed to housing 71
and extends inwardly toward the axis of inner race 48. A drive
shaft 83 is journalled to bracket 81 and extends into the plane of
the inner race 48. A drive roller 82 is mounted on shaft 83 and
contacts inner race 48. A drive gear 84 is mounted on shaft 83
coplanar with the downstream drive gear 86. A chain 85 connects
gears 84 and 86. Therefore, the relative rotation of inner race 48
and dispenser barrel 50 will drive the drive wheel 82, the
downstream roller 74, and the upstream roller 72 all to rotate in
the same direction. The ratio of gears 84 and 86 is preferably 1:1
for the sake of convenience although other predetermined ratios may
be utilized. As barrel 50 rotates, roller 82 will pass by roller
69. The width and position of the rollers 69 and 82 should be
chosen so the rollers do not collide during rotation.
As shown in FIG. 13, free rollers 121, 122 and 123 are journalled
to plate 79 and housing 71 adjacent the roller 72 and 74. As shown
in FIG. 4, the film web 58 is drawn from film roll 56 across first
free roller 121, then across the surface of downstream roller 72,
and across second free roller 122 adjacent the space between roller
72 and 74, across the downstream roller 74, and across free roller
123. Film web 58 is drawn as far as the downstream roller 74 by the
relative rotation of race 48 and barrel 50, and then across roller
123 to the applicator mandrel 180 by relative rotation of barrel 50
and the mandrel 180. All of the rollers 72, 74, 121, 122 and 123
rotate as the film web passes across them, and are parallel to the
film roll 56 and the barrel tubes 53. A nonparallel angled free
roller 124 may be mounted to hoops 52 and 54 adjacent free roller
123. Film web 58 passes from free roller 123 across roller 124 and
then to the center of barrel 50 in the vicinity of bundle 40 and
applicator mandrel 180. The angular placement of roller 124
advantageously enhances wrinkle-free application of the film web 58
at the mandrel. Roller 124 preferably is mounted so that the angle
may be adjusted to obtain the optimal film condition. The stretched
film web 58 is drawn during rotation of the dispenser barrel 50 to
applicator mandrel 180 through which bundle 40 is transported
during wrapping. As shown in FIG. 22, the mandrel 180 comprises a
film web transporter 108 beneath the bundle conveyor 110, and at
least one film web transporter adjacent at least one additional
side of the bundle such that two film web transporters carry the
film web adjacent opposed surfaces of the bundle. Bundle conveyor
110 preferably includes one or more endless loop package chains 102
circulating around chain tracks 103. Chain tracks 103 are spaced
sufficiently far apart in main plate 111 of conveyer 110 to avoid
bundle spillage, and are preferably manufactured from a class of
plastic substances known as ultrahigh molecular weight
polyethylene. Chain tracks 103 expose the uppermost surfaces of
chains 102 and support the lower surface of chains 102 against sag
when a bundle 40 rests on chains 102. At a point upstream of
dispenser barrel 50, each chain 102 circulates around a gear 112
mounted to an axle 122, then around a gear 114 mounted to an axle
124, and finally around a gear 116 mounted to an axle 126, before
proceeding downstream to carry the bundle. Main plate 111 of
conveyor 110 defines a throughgoing bore 128 beneath each track
103, through which the returning chain 102 passes to encounter gear
112.
Film web transporter 108 is positioned beneath the conveyor 110 and
preferably includes an endless loop chain 132 circulating in a
downstream direction in chain track 109 beneath the plate 111 and
then returning in an upstream direction through a throughgoing bore
134 defined by plate 111. At the upstream end, chain 132 circulates
around gear 136 mounted to axle 122. In this manner, the bundles 40
are carried on conveyor 110 synchronized at the same speed as the
film web carried beneath conveyor 110 by transporter 108. This is
accomplished by using identical gears 112 and 136 on shaft 122 to
drive chains 102 and 132.
As shown in FIG. 2, conveyor 110 and transporter 108 may be driven
by mounting gear 196 to axle 194 of motor 195. Gear 197 is mounted
on axle 122. Chain 198 circulates about the gears 196 and 197, so
that operation of the motor 195 will move the chains 102 and 132
which engage gears 112 and 136, respectively.
At the downstream end of the conveyor 110, each chain 102 passes
across the end of track 103 and around a gear 130 mounted to freely
rotate so that the chain 102 passes from the upper track 103
flowing in a downstream direction to the throughgoing bore 128
flowing back upstream, in the reverse direction. Chain 132
circulates about a gear, not shown, mounted to main plate 111
between the two gears 130. Wheels 200 are mounted downstream from
gears 130 on plate 111 and rotate freely with gears 130
sufficiently below the upper surface of main plate 111 to avoid
contact with the bottom of a bundle. In order to support the
downstream end of conveyor 110 and film web transporter 108, the
bottom edge of each wheel 200 is supported on roller 201 attached
to the frame. Thus, the film web is carried downstream beneath main
plate 111 by the lower exposed portion of chain 132. The film web
does not encounter any opposition to this motion since the portions
of chains 102 and 132 moving upstream are isolated within bores 128
and 134, respectively. When the film web transported by chain 132
encounters the wheels 200, it passes between the wheels 200 and the
roller 201 and recovers against the bottom of the bundle downstream
from the wheels and the roller.
The applicator mandrel 180 includes a bottom film web transporter
108 and at least one other film web transporter which is adjacent
at least one widest surface of the bundle in addition to
transporter 108. If the widest bundle sides are vertical, then two
parallel vertical transporters 210 are preferably utilized as shown
in FIGS. 1 through 4. If the widest sides are horizontal, then one
film web transporter 330 is placed atop the bundle and opposite
transporter 108 as shown in FIGS. 19 through 21. Each film web
transporter carries the film web 58 wrapped across the film web
transporter in the downstream direction at the same speed as the
bundle speed.
The film web transporters 108 also provide an effective increase in
the wrapping radius perpendicular to the widest bundle surface.
Thus, the difference between the vertical wrapping radius and the
horizontal wrapping radius of an oblong bundle during wrapping is
minimized by placement of the film web transporters so that the
cross-section of the film web is supported on the mandrel is less
oblong and more square than the bundle cross-section. The variation
in elongation of the film web as the film web is wrapped across
consecutive surfaces of the application mandrel 180 is more unified
and is more easily maintained substantially in the linear wrap
force range according to the present invention by this positioning
of application mandrel 180. High containment force is obtained at
the mandrel and ultimately at the bundle.
The applicator mandrel 180 preferably extends through both
dispenser barrels 50. However, a first mandrel may extend within
the first dispenser barrel and a second mandrel may extend within
the second dispenser barrel. Alternatively, conveyor 110 and
transporter 108 may extend through both barrels while film web
transporter 210 or 330 are separately positioned in each
barrel.
Certain types of bundles are extremely fragile and may require film
web transporters which extend to cover the entire adjacent bundle
surfaces for preventing the wrapped film web from imparting a
substantial part of the wrap force on the bundle. However, for many
other less fragile bundles, significant economy can be derived by
covering only a portion of a bundle surface with a film web
transporter, leaving the bundle edges exposed to encounter film web
58. Since the topmost lengthwise edges of the bundle are most prone
to disalignment, film web transporters 210 or 330 preferably extend
across bundle surfaces to a distance from bundle edges no greater
than 1/2 of the height or width, respectively, of bundle units at
each edge.
The effect of this placement on film demand is shown in FIG. 16 in
which a rectangular bundle with 10 inch vertical surfaces and 14
inch horizontal surfaces is placed between a top surface film web
transporter 330 and the conveyor 110 and bottom surface film web
transporter 108. For purposes of illustration, it is assumed that
the film web transporters are 2 inches thick. At the downstream end
of the transporters, the film web recovers to the top and bottom
surfaces of the bundle, and the final circumference around the
bundle is 48 inches.
With very fragile bundles, the film web transporters preferably
extend across the full 14 inch width of the top and bottom bundle
surfaces in the applicator mandrel. In this case, the mandrel
wrapping circumference is 56 inches and the film web recovers by
16% to reach the final circumference of 48 inches at the downstream
end of the applicator mandrel when it moves from the mandrel to the
bundle. Furthermore, the maximum wrapping radius B is 9.9 inches
and the minimum radius A is 7 inches, with a ratio of minimum to
maximum of 0.71 and a difference of 2.9 inches. Thus, the placement
of the film web transporters present a wrapping cross-section which
reduces the range of elongation variance during wrapping of the
applicator mandrel.
As shown in FIG. 17, as preferred for somewhat less fragile
bundles, the width of the film web transporters and conveyor is
reduced to 10 inches to obtain an octagonal cross-section in the
applicator mandrel for wrapping with both the bundle edges and the
film web transporter edges encountering wrapped film web 58. The
wrapping circumference of the applicator mandrel is then 51.3
inches, and the film web must recover only 6.9% to reach the final
bundle circumference of 48 inches. The maximum wrapping radius is
reduced to 8.6 inches, so that the minimum to maximum ratio is
increased to 0.81 and the difference or range of radii is reduced
to 1.6 inches. Thus it is apparent that a very modest reduction in
the transporter width achieves significant improvement in final
bundle force after recovery by the film web beyond the downstream
end of the applicator mandrel, while simultaneously requiring a
linear wrap force range of lesser width and permitting higher
pre-stretch ratios. It is useful to reduce the width of each
transporter so that its outermost edges are at a radius, or
distance, from the center of dispenser rotation no greater than the
distance from the dispenser rotation center to the bundle edges as
shown in FIG. 17.
While those skilled in the art will recognize that the precise
calculations will vary depending on the thickness of the film web
transporter and the cross-section dimensions of the bundle, it can
be seen that significant advantages are achieved in both final
force and final film elongation by the present invention, which in
turn reduces the operating consumption and total cost of the film
web.
As shown in FIG. 9, by comparison, the 10 inch by 14 inch bundle
conventionally would be supported only by a 10-inch-wide conveyor
110 and bottom film web transporter 108. Presuming that the bottom
supports 108 and 110 total 2 inches in height, that the bundle is
centered and that the film web recovers between the dispenser and
the bundle, then the maximum wrapping radius B is 9.2 inches while
the minimum radius A is 6 inches, for a ratio of 0.65 and a
difference of 3.2 inches. The recovery at each side is thus at
least 35% during wrapping and an additional 3.2% (49.6 inches to 48
inches) when the bundle exits the conveyor, with additional
recovery between the pre-stretch subsystem and the bundle of 33% to
50%.
Generally, the width of the conveyor 110 may be reduced where the
bundle rests in a tray during wrapping. This is often the situation
when wrapping for example, cases of soft-drink cans or bottles, or
where a single, relatively stiff unit comprises the bottom of any
wrapping cross-section. In the illustrated mechanism, the mere use
of chain as a minimum-width film transporter 108 presents a modest
further reduction in final recovery at the end of application
mandrel 180 but does not further decrease the range of wrapping
elongation variance since the demand speed maxima and minima remain
constant. The width of top film web transporter 330 may be reduced
so that the edges of transporter 330 preferably span at least half
of the width of outermost top bundle units in the horizontal
direction transverse to the motion of the bundle. Likewise, the
height of transporters 210 preferably spans at least half the
height of outermost top bundle units.
Alternative film web transporters beneath the bundle are described
in U.S. Pat. No. 4,317,322 assigned to Lantech, Inc. and
incorporated by reference in this application.
FIGS. 2 through 4 show a film web transporter arrangement which is
preferable when the wider side of an oblong bundle is vertical.
Film web transporters 210 are positioned in close proximity or in
contact with opposing widest surfaces, which are vertical, of the
tall bundle 40. Each film web transporter 210 comprises a
skid-sleeve 178 secured to the frame, and upstream double-sheave
pulley 172 and downstream pulley 174 mounted at opposite ends of
the skid-sleeve 178. A belt or chain 170 encircles one sheave of
pulleys 172 and 174. Belt 170 circulates in a downstream direction
toward pulley 174 while exposed at an upper edge of skid-sleeve 178
toward pulley 172. Upstream pulley 172 is preferably located
upstream from the wrapping station 41, while the skid-sleeve 178
preferably extends downstream through and beyond the wrapping
station. Generally, each skid-sleeve 178 extends vertically across
an entire vertical face of bundle 40, but for sturdy bundles may be
abbreviated to extend across merely a portion of the bundle
face.
Transporter motor 162 is mounted to a lower portion of frame 38,
and rotates motor shaft 164 about its axis. Shaft 164 extends
outwardly on opposite sides of motor 162. Pulleys 168 are mounted
to opposite ends of axle 164 below respective pulleys 172. Each
pulley 168 and a second sheave of the respective pulley 172 are
encircled by a vertical belt 169. Therefore, operation of motor 162
will drive the circulation of side conveyor belts 170. As the upper
portion of each belt 170 moves downstream, it carries with it any
film web 58 which may be wrapped around the skid-sleeve 178. The
skid-sleeve 178 is preferably configured and composed of a material
chosen for low friction with the film web 58.
FIGS. 19 through 21 show a film web transporter arrangement which
is preferable when the wider side of an oblong bundle is
horizontal. A top conveyor 330 is driven to carry film web 58 is
wrapped along the top of the conveyor 330 in said downstream
direction at the same speed as the bundle. The top conveyor 330
comprises belts or chains 332 rotating across upstream rollers 334
and downstream rollers 336, beneath conveyor support plate 338. The
rollers 334 and 336 are journalled to the support plate 338.
Support plate 338 extends upstream from the wrapping area and is
fixed to the frame of the apparatus to support top conveyor 330.
Motor 340 and dual output reducer 344 are mounted to frame 38
upstream of the wrapping area. Motor shaft 342 is coupled to
reducer 344, and the output shafts of reducer 344 are coupled to
rollers 334. Motor 340 will drive rollers 334 to rotate in opposite
directions and move the outer portions of belts 332 downstream with
the bundle.
Other greatly preferred film web transporter arrangements are shown
in FIG. 16 and 17. Belts or chains 332a and 132a form the edge
surfaces of the film transporters 108 and 330 to suspend the film
web between them. This arrangement has proven especially useful in
defining the mandrel for wrapping fragile bundles.
This construction allows the film web to be wrapped around a bundle
40 carried from the infeed conveyor 31 onto the wrapping station
41. The stretched web is initially wrapped around the bottom
transporter 108 and either two side conveyors 210 or a top conveyor
330, with both the bundle and wrapped film web being carried by the
conveyor assembly and transporters in the same direction. The film
web applied to mandrel 180 forms a tube which moves off the the
downstream end of mandrel 180 and recovers, still under tension
onto the bundle 40 emerging from within the mandrel. Even if the
application mandrel is wrapped with a very high wrap force, the
uniform partial recovery of film web allows fragile bundles to
experience balanced forces on opposing surfaces which are reduced
from those on the application mandrel. This avoids bundle collapse
which would have occurred using conventional arrangements at high
wrap forces.
As shown in FIG. 18, the bundles 40 preferably are spaced apart so
that the continuous film web tube between consecutive bundles can
be severed by any conventional cutting device 400 downstream of the
mandrel 180. Continuously wrapped bundles are taken off of the
apparatus and are severed into separate bundles on conveyor 33 away
from the apparatus. According to the present invention, the film
web tube portions extending before and behind bundles after
severance promptly recover under tension against respective leading
and trailing ends of the attached bundle to form tight bull's-eye
patterns 40a on the ends of the bundle. The containment force
exerted on bundle ends is improved due to the higher force applied
when the film web encompasses the bundles and the spaces
therebetween.
Infeed conveyor 31 brings each bundle 40 onto conveyor 110 which
then carries the bundle through each of the two wrap stations 41
within the applicator mandrel 180. At startup, the leading edges of
the film webs 58 are held beneath transporter 108. One way to hold
the webs at startup is to tie the leading end of the web 58 from
stage 35 to the leading end of the web 58 from stage 36 beneath
transporter 108. As shown in co-pending application Ser. No.
582,779, each dispenser 41 is positioned and arranged to orbit the
applicator mandrel in a direction opposite that of the other
dispenser 41, so that the two wrap patterns placed on each bundle
will have opposite circular components due to the orbiting
dispensers and identical linear components due to the motion of the
mandrel and bundle.
As each barrel 50 rotates, film is drawn across the surface of
downstream roller 74 to encircle the applicator mandrel 180. The
rotation speed of roller 74 is proportional to the rotation speed
of the race 44 and independent of the demand for film web 58 at the
bundle. If chain 77 engages gears 76, 78 and 87, then the rotation
speed of upstream roller 72 is held to a constant ratio of that of
downstream roller 74, so that upstream roller 72 draws film 58 from
film roll 56. The film web is stretched both during passage between
the rollers 72 and 74, due to their relative speed ratio, and
between roller 74 and the applicator mandrel. Alternatively, roller
72 can be removed or allowed to freewheel by removing chain 77 or
by disengaging gear 76 through a clutch mechanism so that no
pre-stretch is exerted on web 58 but the web 58 is still drawn to
and dispensed across roller 74 at a substantially constant supply
speed and is stretched between roller 74 and the mandrel.
At the improved operating speed of barrel 50, which is typically 40
to 60 rpm, the high demand speed of film web 58 at mandrel 180
causes elongation of web 58 at the mandrel substantially beyond the
yield point of the film web between the film web dispenser and the
applicator mandrel. The stress-strain characteristics of the film
web in this area are within the corresponding linear wrap force
range. The direction of the wrap force varies as the film web
dispenser orbits the applicator mandrel 180. However, applicator
mandrel 180, which includes conveyor 110 and transporter 108 in
combination with transporter 330 or transporters 210, supports the
bundle and resists the force from any of its directions.
Thus, the present invention achieves significantly increased
operating speeds without compromising reliability or increasing the
rate of failure of the film web. The film web remains intact even
if a hole develops in the film web. This is because the controlled
supply system will continue to dispense film independent of its
being weakened by the hole. Thus, no dispenser or pre-stretch
mechanism shut-down occurs.
After one wrap has been made around the mandrel 180, the leading
edge of the web 58 is held firmly beneath the overlying web 58. A
number of wraps are placed around the mandrel which carries the
wrapped web and the bundle downstream. The combination of dispenser
circular motion and mandrel/bundle linear motion creates a helical
wrapping pattern with a first circular component at the first
dispenser and a second circular component, opposite to the first,
at the second dispenser. It should be noted that there is a space
between the downstream end of applicator mandrel 180 at the second
wrapping stage and the take-off conveyor 33 allowing the stretched
film web to recover from the larger mandrel circumference to the
smaller circumference of the bundle emerging from the mandrel,
applying opposing forces simultaneously to opposite bundle sides.
The reduction in web circumference is accompanied by a reduction in
bundle force, thus avoiding the bundle crushing and the film web
failure experienced at peak forces in the prior art.
In the continuous wrapping operation, the bundles are continuously
carried along the wrapper conveyor assembly to the end of the
applicator mandrel, and then onto take-off conveyor 33. The bundles
are then severed between the spaced film areas as previously
discussed and taken away to another transport area.
The present invention is directed toward a process which avoids the
dilemma of simultaneous high-force hazards of film web rupture and
low-force inefficiencies due to unreliable containment present in
conventional wrapping systems. It does so by managing the supply
speed and stress-strain characteristics of the film web and
preventing the force on the film web from controlling the supply
speed of the film web from the film web dispenser. The process
markedly increases the final containment force of the film web on
the bundle, reliably avoids both bundle failure and film web
failure during wrapping, minimizes wrinkles in wide film web, and
permits operation at higher throughput and film web speeds than
previously possible in conventional systems.
In accordance with the present invention, there is provided a
process for wrapping a bundle 40 with the film web 58 dispensed
from a film web dispenser 70 comprising moving the bundle 40 into
an applicator mandrel 180, revolving the film web dispenser 70
relative to the applicator mandrel 180, dispensing the film web 180
from the film web dispenser 70 onto the applicator mandrel 180 at a
constant supply speed, transporting the film web 58 wrapped around
the applicator mandrel 180 beyond the downstream end of the
applicator mandrel 180, continuing moving the bundle 40 beyond the
downstream end of the applicator mandrel, and applying the film web
58 from the applicator mandrel 180 onto the bundle 40 so as to
provide a containment force in the film web 58 after it has been
applied onto the bundle 40.
The supply speed of the film web at the film web dispenser is
preferably prevented from increasing by restraining and retarding
the film web being dispensed by the film web dispenser at a
dispenser supply speed less than the lowest demand speed at the
applicator mandrel.
According to the present invention, the film web is stretched
between the film web dispenser and the applicator mandrel. Such
stretch can be identified by observing a film web marked at regular
intervals which are spaced farther apart on the wrapped objects
such as the applicator mandrel than between the pre-stretch rollers
in the film web dispenser.
FIG. 5, shows that the speed of film take up or demand at the
wrapped object indicated by the curve 150, varies as the barrel 50
rotates about the rectangular mandrel 180 and bundle 40. In
particular, a minimum point 152 occurs as each edge is encountered
and is followed by a maximum point 154.
FIG. 6 illustrates a film payout speed or supply function,
indicated at 162, which is exhibited by the present invention at
the downstream roller 74 of the film web dispenser. This shows that
the supply function is substantially constant or flat even at the
high speeds of operation. Regardless of the demand for film at the
bundle, the supply speed of film at the downstream roller 74 is
controlled so as to remain constant while barrel 50 and race 48
each operate at constant speed.
FIG. 7 illustrates a curve of the force and elongation of the film
web on the bundle in which film web force and elongation is locked
in at each bundle edge at each minimum point 142 below the prior
maximum point 144 where elongation was greatest. In conventional
bundlers, elongation at the wrapped object fluctuated in a similar
pattern. However elongation was always less than pre-stretch
elongation. Also, the the maximum force corresponding to point 144
was always reduced by the mechanical advantage or motor torque of
the pre-stretch devise to a force substantially less than the force
exerted on the film web between the pre-stretch rollers.
In accordance with the present invention, the film web is stretched
beyond its yield point to plastically deform the film web between
the film web dispenser and the applicator mandrel throughout the
revolution of the film dispenser about the applicator mandrel. It
is further in accordance with the present invention to maintain the
film web between the film web dispenser and the applicator mandrel
in the linear stress-strain range beyond the yield point throughout
the revolution of the film dispenser wherein the film web stress
undergoes minimal variation while film web strain undergoes
comparatively greater variation throughout the revolution of the
film dispenser while the film web is positioned between the film
web dispenser and the applicator mandrel.
In accordance with the present invention, if the bundle is
substantially oblong in cross-section, the film web is prevented
from substantial pre-stretching prior to dispensing the film web
from the film web dispenser. However, with bundles less oblong in
cross-section, the film web is pre-stretched beyond its prestretch
yield point to plastically deform the film web in the film web
dispenser prior to subsequently post-stretching the film web beyond
its post-stretch yield point to further plastically deform the film
web between the film web dispenser and the applicator mandrel.
When initial stretch beyond the pre-stretch yield point range of
141 of film web 58 is isolated between upstream roller 72 and
downstream roller 74, secondary stretch between the downstream
roller and the applicator mandrel causes the film web 58 to follow
a force-elongation curve 275, illustrated in FIG. 14. This curve
exhibits a secondary linear wrap force range 277 between the
secondary yield point range 241 and the break point 249. The
secondary yield point 241 is found at elongations and forces
slightly lower than at pre-stretch operating point 148, and
increases when pre-stretch elongation is increased. The range 277
generally is found at higher elongations and lower forces than the
pre-stretch operating point 148. The present invention preferably
utilizes a portion of the linear wrap force range 277 exemplified
by the minimum 276 and maximum 278. Force and elongation are locked
in at minima 276 and, as the bundle and film web moves beyond the
applicator mandrel, recovery produces a bundle force and elongation
at recovery point 279, well above the final force and elongation at
point 142 which was that at which conventional processes
operated.
To perform the process of the present invention without
prestretching the film web, upstream roller 72 is allowed to
freewheel by removing chain 77 or otherwise decoupling gears 76 and
78 in any well-known conventional manner. Alternatively, roller 72
could be removed. This results in a different stress-strain
relation on the film web between the downstream roller 74 an
application mandrel 180. In accordance with the present invention,
if the film web is stretched only between downstream roller 74 and
applicator mandrel 180 its stress-strain relationship is shown in
FIG. 15 as curve 273. This curve exhibits a broad yield point
region 272 followed by a broad linear wrap force range 271 during
which plastic deformation occurs in the film web. This linear wrap
force range is broader than the linear wrap force range 277 for
pre-stretched film.
In this non-pre-stretched situation, where initial stretch occurs
over a long film path, the web width is reduced considerably during
stretch between the dispenser and applicator mandrel 180. This
phenomenon is known as neckdown. Neckdown can be sharply inhibited
by pre-stretching the film web between closely spaced rollers prior
to wrapping the film web on applicator mandrel 180. The force level
or stress in range 271 is generally lower than at pre-stretch film
webs in pre-stretch operating point 148 or range 277. The linear
wrap force range 271 extends between the broad yield point range
272 and the break point 250 over a wider variation of strain
elongation. Yield point range 272 occurs at a slightly lower strain
elongation and force level or stress than the pre-stretch yield
point 141 between rollers. According to the present invention, it
is preferable that in the non-pre-stretch embodiment, elongation is
varied between exemplary maximum 270 and minimum 274 as each side
of the applicator mandrel is wrapped. Force and elongation are
locked in at each minimum 274. As the bundle and the the web move
beyond the applicator mandrel 180, recovery of the film web onto
the bundle produces film web stress-strain conditions at point 280.
While strain elongation at point 280 without pre-stretch may or may
not be as great as that of conventional processes, depending on the
contour of the applicator mandrel, containment force of the film
web on the bundle 40 is significantly improved.
According to the present invention, the film web is dispensed from
downstream roller 74 at a constant supply speed. Downstream roller
74 of the film web dispenser and thus the film web is restrained
sufficiently below the lowest takeup or demand speed at applicator
mandrel 180 to apply stretch to the film web between the dispenser
and the mandrel substantially within the gentle sloped linear wrap
force ranges 271 or 277 of the respective curves 273 and 275,
depending on whether or not the film is pre-stretched. Due to the
gentle slope of the curve in this range, the mandrel 180 as well as
the film web and thus the film web dispenser experiences a
substantially constant wrap force regardless of variation in
elongation due to the varying demand for film web as it crosses the
mandrel edges during wrapping. The applicator mandrel then releases
the film web to encompass each bundle at a non-crushing bundle
containment force lower than the wrap force on the mandrel due to
the decrease in cross-section from mandrel to bundle.
As the initial pre-stretch ratio exerted between upstream roller 72
and downstream roller 74 is increased, the stress force level of
the secondary linear wrap force range 277 will increase, neckdown
of the web between the downstream roller and the mandrel will
decrease, and the span of secondary elongation within the range 277
will decrease. Conversely, reduction of the prestretch ratio will
decrease the secondary constant wrap stress force level, increase
neckdown, and increase the "width," or range of stretch, of the
linear wrap force range 277. Therefore, the process is preferably
used at lesser pre-stretch when wrapping wider or taller mandrels
and delicate bundles that require low force. The rotation rate of
inner race 48 is adjusted in order to raise or lower the supply
speed of the film web, in order to accomodate a change in demand
rate for bundles of a different shape or size. It may also be
necessary to configure the applicator mandrel to extend entirely
across bundle surfaces of delicate bundles, so that the mandrel
incurs a large portion of the wrap force.
While the use of pre-stretched film web is more economical, film
web with little or no pre-stretch may be useful where the oblong
bundle configuration causes extreme web takeup speed variations. In
such situations, the wide linear wrap force range 271 of stretch of
non-pre-stretched film web accommodates the takeup speed
variations.
Certain types of bundles show extreme differences in height
relative to width. These include both extremely tall bundles and
extremely wide bundles. Such bundles exhibit the most extreme
variations in web takeup speed and require the widest linear wrap
force ranges 277 or 271. An ideal bundle without stretch variation
would offer a circular wrapping cross-section centered on the axis
of revolution of the dispensers. Among rectangular bundles, a
square cross-section centered on the axis of revolution of the
dispensers exhibit minimal variations in takeup speed and secondary
stretch. According to the present invention, the wrapping
cross-section experienced by the film web is modified in order to
minimize differences between height and width, and thereby minimize
fluctuations in elongation above the yield point. At the same time,
this system advantageously prevents disruption of the multi-unit
bundle by the high, though constant, wrap force.
Cross-section adjustment is accomplished by placement of applicator
mandrel 180 in the wrapping area surrounded by barrel 50,
preferably centered on the revolution axis of race 44.
One way to confirm that the system is stretching the film web in
its linear wrap force range between the dispenser and the
applicator mandrel is to establish the stress-strain curve of the
film web by dispensing the film web through a load cell between the
dispenser and the applicator mandrel while observing the elongation
of the film web. After knowing the range of the linear wrap force
region of the curve, the controls of the dispensing mechanism can
be set to provide the stress and strain on the film web necessary
to place it in the linear wrap force region.
In accordance with the present invention, this system of stretching
provides higher final stretch, higher bundle containment force on
the film web, higher throughput, and use of less uniform film while
preventing film web breakage than were previously through possible.
Such web stretch at the wrapped object, as opposed to web recovery
minimizes wrinkles in a wide web, conserves film by establishing
containment with fewer web layers, and provides a tight bull's-eye
in the film web at the ends of the bundle.
In accordance with the present invention, the film web is
pre-stretched in the film web dispenser at a sufficient prestretch
force and mechanical advantage so that it is beyond its pre-stretch
yield point and subsequently further elongated by post-stretching
the film web between the film web dispenser and the applicator
mandrel beyond its pre-stretch yield point at a post-stretch force
which is less than the pre-stretch force and greater than the
pre-stretch force reduced by the mechanical advantage of the
pre-stretch system. It is preferable to maintain the film web
beyond its post-stretch yield point throughout the revolution of a
film dispenser while the film web is positioned between the film
web dispenser and the applicator mandrel. Under these conditions,
the present invention avoids the overrun condition which occurs in
conventional pre-stretch dispensing systems when the wrap force
exceeds the pre-stretch force reduced by the mechanical
advantage.
As shown in FIG. 26, the supply speed control mechanism of the
present invention prevents the supply speed of the film web from
increasing and also prevents the supply speed of the film web from
decreasing. This is accomplished by using a motor driving the
rollers of pre-stretch device which is controlled by a speed
control device with regenerative capabilities which can prevent the
speed of the motor from increasing as well as decreasing. Although
motor controllers with regenerative capabilities are known in the
motor control art, conventional wrapping devices did not have a
control which prevented the supply speed from increasing, but
rather only had a control that prevented the supply speed from
decreasing. A motor control with regenerative capabilities would be
known in the motor control art as a two quadrant controller since
it could drive or retard a motor in a controlled fashion which is
turning in a positive forward direction. Motor control used on
conventional wrapping devices would be known in the motor control
art as a single quadrant controller since it could only drive, and
not retard, a motor in a controlled fashion which is turning in a
positive forward direction.
The positioning of the applicator mandrel according to the
teachings of the present invention accomplishes many of the objects
of the present invention. Since the film is wrapped around the
applicator mandrel, higher film force may be used to prevent
crushing, twisting, dislodging or shifting which would occur in
conventional arrangements. According to the present invention, when
the film web tube formed on the applicator mandrel is released to
surround each bundle it is done so by contacting the bundle on
opposing surfaces simultaneously rather than exerting force on
single bundle edges and sides so that wrap forces are mutually
opposing and balanced. Also according to the invention, by
suspending the film web on an applicator mandrel, forces are locked
in on the film web on different sides of the applicator mandrel.
Transferring the film web in its suspended state from the
applicator mandrel to the bundle, the film web reduces the
difference between the locked in forces on its sides, therefore
retaining more even locked in containment forces on the various
sides of the bundle. This is especially true when either or both
the bundle and the applicator mandrel have oblong
cross-sections.
Considerations of dislodging, crushing, and good containment
characteristics of a film web at the end of the wrap bundle, such
that a tight bull's-eye is provided, it is especially important
when wrapping a bundle having a plurality of bundle units.
According to the invention, it is preferable in such circumstances
to position the plurality of bundle units to form a bundle having
as square a cross-section as possible.
In accordance with the present invention, problems with grossness
of load and point source loading which have a tendency to rupture
the film web in conventional systems, are prevented through the
uniformity and controllability of the shape of the applicator
mandrel. Further, the surface of the applicator mandrel is such
that a substantially uniform force is applied across the full width
of the film web while dispensing the film web onto the applicator
mandrel. Although the applicator mandrel may contain linear edge
lines in some embodiments, there are no corners, which would
otherwise be present from the bundle which give rise to destructive
point source loading at high wrap forces.
In addition, in accordance with the present invention, the
grossness of load problems are solved by wrapping bundles of a
sufficiently small size such as those that can be grasped and
carried by a person and constitute a unit of a pallet load, and
such as bundles in which the greatest cross-sectional measurement
is not substantially greater than two feet square. Also in
accordance with the present invention, bundles of uniform
cross-section are used when continuously wrapping bundles with a
system such as the dual stage orbiting dispensers.
According to the present invention, high throughput is possible
since the film web dispenser can be revolved around the applicator
mandrel and the bundle above the 25 revolutions per minute
previously thought to be a maximum while using conventional
systems. According to the present invention, the film web dispenser
is revolved around the applicator mandrel on the bundle at a rate
of at least about 30 revolutions per minute and is preferably
operated in a range of about 40 to 60 revolutions per minute.
Additional advantages and modifications will readily occur to those
skilled in the art. The invention in its broader aspects is,
therefore, not limited to the specific details, representative
apparatus and illustrative examples shown and described.
Accordingly, departures may be made from such details without
departing from the spirit or scope of applicants general inventive
concept.
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